Iron and iron-based metal alloys such as mild steel as well as copper and other yellow-metal alloys are well known materials used in constructing the circulating pipes and devices in aqueous systems. Typical devices include evaporators, single and multi-pass heat exchangers, cooling towers, and associated equipment, and the like. As the system water circulates through the system it passes over or through the iron-based or yellow-metal devices, and a portion of the system water evaporates causing an increase in concentration of the dissolved salts and minerals in the water. These salts and minerals approach and reach a concentration at which they may cause severe pitting and corrosion which eventually requires replacement of the iron-based or yellow-metal parts. Various corrosion inhibitors have been previously used.
Chromates and inorganic phosphates or polyphosphates have been used to inhibit the corrosion of metals which is experienced when metals are brought into contact with an aqueous system. The chromates, while effective, are highly toxic and thus present handling and disposal problems. Phosphates are nontoxic, however, due to the limited solubility of calcium phosphate, it is difficult to maintain adequate concentrations of phosphates in systems containing dissolved calcium salts. The polyphosphates are also relatively non-toxic, but then tend to hydrolyze to form orthophosphate which, like phosphate itself, can create scale and sludge problems in the form of calcium phosphates.
N-Tributyl Tetradecyl Phosphonium Chloride (TTPC) has been used previously as an antibacterial and biocide agent for use in water treatment systems (Canadian Patents No. 1,262,084 and 1,262,667, U.S. Pat. Nos. 4,835,143, 4,835,144, and 5,010,066). These patents do not teach the addition of cationic alkyl-phosphonium salts as corrosion inhibitors for ferrous and copper containing alloys in aqueous systems as an individual corrosion inhibiting component or in conjunction with other commonly used corrosion inhibitors.